First of all, you have mixed content on your site which means that on those pages, you will NOT serve https pages, which in turn means that those pages miss out on the speed benefits that https offers.

2) Fix browser caching
3) Work on fixing Defer parsing of JavaScript (move as many JavaScript files to the footer as you can.
4) Serve Scaled Images
5) Minify your JS & CSS
6) I suggest using the addon WP Total Cache to do the bulk of the work.

I did some quick glance on your website - I don't feel like it would be fair to give you to criticize you a lot without giving any suggestions, but you do need to do something with the images and script in the first place. As was recommended above you could move vast of the scripts down into the footer, but I don't think of it as the practice well enough - make them asynchronous first of all. And most of your images are too large as well as minify CSS

I just looked at one of my... sigh... very ugly WordPress sites which contains a massively bloated list of plugins with massive database i/o thrash.

This site's HTML component produces first time load of 250ms for DNS + 200ms for HTML component, so subsequent site visits load HTML in roughly 200ms.

This is typical of a well tuned WordPress site.

And now, the bad news.

You'll likely have to change hosting + go through some serious site tuning to produce consistent high site speed.

Who you contact to do this work, will depend on your site cashflow, as Server Savants tend to be expensive + fast/stable WordPress hosting tends to be expensive.
If you have some Server Savant skill, search for other posting comments I've made, as many of these postings contain good information from many people with differing views.

Pick an approach which seems most useful for your situation.

Like help speeding up your site? Skype me @ ID davidfavor for a quote. Be sure to include your site name in your Skype Add Contact request.

Your javascript and css files are not minified and concatenated. This is probably the hardest part of the optimization process because all kinds of javascript dependency issues might appear while trying to implement that.